How soon will it be before my house starts to flood?

River Severn Data for Ironbridge.

Complete the river data log below A to F. (The spreadsheet graphs have been saved in Excel format for your use)

When you have completed all of the six sections you will be able to see if your house will get flooded, and if it does, by how much.

 

A. THE RAINFALL

This is how much rain falls in the storm.

Complete the graph and add the following labels:

Start of Storm (S), Peak (P), End of Storm (E).

Spreadsheet graphs

Data

1 4 mm
2 20mm
3 8 mm
4 4 mm
5 0 mm
6 0 mm
7 0 mm

 

B. THE RIVER RESPONDS

This is how the river flood water level rises after the storm.

This sort of graph is called a HYDROGRAPH (spreadsheet graphs).

Complete the graph using the data provided and add the following labels. 

PEAK (P), RISING WATER LEVEL (R), FALLING WATER LEVEL (F), BASE FLOW (B), TIME LAG (L)  

DATA 

1 0.4
2 0.4
3 0.4
4 0.4
5 0.6
6 0.8
7 1.2
8 1.8 
9 2.0
10 2.4
11 2.2
12 1.8
13 1.8
14 1.6
15 1.4
16 1.4
17 1.0
18 1.0
19 0.8

 

Note: The normal winter level of the river (Base Flow) is on average flowing at 0.4 cubic metres of water per second. At the end of the storm it took 36 hours to get back to it’s average level at 0.4 M3 /sec

Summary:

Explain what has happened to the river discharge and reasons for any pattern you notice.

 

C. CROSS SECTION SURVEY DATA  

This is the shape of the flooded river at the peak of the storm.

Study the completed cross section.

Calculate

(a) The CROSS SECTIONAL AREA =  ………… square meters.

(b) The distance along the Wetted Perimeter. This is were the water comes in  contact with the bank and stream bed. Marked on the diagram in red and two arrows.

The distance along the WETTED PERIMETER = …………… meters.

HINT: It is simply a mater of counting squares in (a) and measuring a distance in (b)

Note that 1 square on the image below equals  2 sq. metres (on the graph shown on the spreadsheet it is 4 square metres)

 

Cross-sectional diagram of the river in full flood. (spreadsheet graphs)

 

D. THE FRICTION IN A STREAM

This is the turbulence of the rapids/white water and the drag effect on the river bank and bed in flood.

Calculate the efficiency of the river channel above. Use this formula:

EFFICIENCY RATIO = Cross sectional  area (a) divided by Wetted perimeter(b)

Note. The higher the value in your answer the more efficient the river is and the less friction is occurring.

At normal level the efficiency ratio is 1.33

E. THE SPEED OF THE RIVER IN FULL FLOOD.

(Five readings were taken over a distance of 50 metres)

1 32 seconds
2 25 seconds
3 18 seconds
4 29 seconds
5 21 seconds

 

Calculate the average speed of the river. (Your computer may have a calculator program)

Total speeds   ______

5                      =  ……  (average speed for 50 metres)

THE AVERAGE SPEED FOR 1 METRE PER SECOND is therefore = ……m/s

 

F. THE RIVER FLOOD DISCHARGE

This is the volume of water in the flooding river.

It is calculated  by:

DISCHARGE (m3/s) = CROSS SECTION AREA (m2) x AVERAGE SPEED (m/s)

(a) Calculate the discharge for the river in flood.

ANSWER =    …………….cumecs (m3/s.

(b) If ONE cubic meter of water equals 1,000 litres of water, how many litres of water will flow down the river in ONE SECOND?

ANSWER =    …………….litres per sec.

 

G. WHAT WILL HAPPEN TO MY HOUSE IN IRONBRIDGE?

We need to know three things:

(a)WILL THE FLOOD WATER REACH UP TO MY FRONT DOOR ?

(b)IF THE FLOOD WATER DOES REACH MY HOUSE, HOW HIGH WILL THE WATER LEVEL BE INSIDE MY HOUSE ?

(c)HOW MANY HOURS DO I HAVE FROM, WHEN IT STARTS TO RAIN, TO WHEN THE RIVER LEVEL STARTS TO FALL?

Calculate the three answers above by using the data in A to F.

The diagram below can be used to see how high the water rises and how it may endanger your house in Ironbridge. (spreadsheet graphs)

 

ANSWERS:

(a)    YES   or   NO  ?  ………….

(b)   (mark and LABEL your answer on the sketch above)

The DISCHARGE in FLOOD is …………….. Cumecs (Cubic metres per second)

(c) …………………….. hours.

 

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